1. Field of the Invention
The present invention relates to an injection apparatus.
2. Description of the Related Art
Conventionally, in an injection molding machine, resin heated and melted in a heating cylinder is injected into the cavity of a mold apparatus under high pressure so that the cavity is filled with the resin. The molten resin is then cooled and solidified so as to obtain a molded article.
The injection molding machine includes a mold clamping apparatus and an injection apparatus. The mold clamping apparatus is provided with a stationary platen and a movable platen. The movable platen is advanced and retracted by a mold clamping cylinder, to thereby perform mold closing, mold clamping, and mold opening.
The injection apparatus includes a heating cylinder for heating and melting resin supplied from a hopper, and an injection nozzle for injecting the molten resin. Further, a screw is disposed within the heating cylinder such that the screw can be rotated and can be advanced and retracted. The screw is advanced so as to inject the resin, and retracted so as to meter the resin.
There has been provided an injection apparatus for an electric injection molding machine in which an electric motor is used to advance and retract the screw.
FIG. 1 is a schematic view of a conventional injection apparatus used in an electric injection molding machine.
In FIG. 1, numeral 2 denotes an injection apparatus, and numeral 4 denotes a frame of the injection apparatus 2. A heating cylinder 21 is fixedly provided in front (left side in FIG. 1) of the frame 4, and an injection nozzle 21a is provided at the front end (the left-side end in FIG. 1) of the heating cylinder 21. A hopper 21b is disposed on the heating cylinder 21, and a screw 20 is disposed within the heating cylinder 21 such that the screw 20 can be rotated and can be advanced and retracted (i.e. moved leftward and rightward in FIG. 1). The rear end (the right-side end in FIG. 1) of the screw 20 is rotatably supported by a support member 5.
Attached to the support member 5 is a metering motor 6 having a speed reduction mechanism. The rotation of the metering motor 6 is transmitted to the screw 20 via a timing belt 7a. 
Further, a ball screw shaft 8 is rotatably supported on the frame 4 in parallel with the screw 20. The rear end of the ball screw shaft 8 is connected, via a timing belt 7b, to an injection motor 9 having a speed reduction mechanism. That is, the injection motor 9 is designed to rotate the ball screw shaft 8. The front end of the ball screw shaft 8 is in screw engagement with a ball nut 5a fixed to the support member 5. Accordingly, by driving the injection motor 9 and rotating the ball screw shaft 8 via the timing belt 7b, the ball nut 5a can be moved axially. A load cell 5b is disposed between the support member 5 and the ball nut 5a. 
In the injection apparatus 2 having the above-described structure, in a metering stage, the rotation generated by the driven metering motor 6 is transmitted to the screw 20 via the timing belt 7a, thereby retracting (i.e. moving rightward in FIG. 1) the screw 20 by a determined amount. At this time, resin is supplied from the hopper 21b, heated and melted within the heating cylinder 21, and accumulated on the front side of the screw 20.
Further, in an injection stage, the rotation generated by the driven metering motor 9 is transmitted to the ball screw shaft 8 via the timing belt 7b, so that the ball nut 5a and the support member 5 are advanced (i.e. moved leftward in FIG. 1) with the rotation of the ball screw shaft 8. As a result, the screw 20 is also advanced, and the resin accumulated at the front side of the screw 20 is injected into the cavity of an unillustrated mold apparatus from the injection nozzle 21a. 
At this time, the force for advancing the ball nut 5a; i.e., the injection force imparted to the screw 20, is detected by the load cell 5b. 
However, in the conventional injection apparatus 2, since the injection force is generated with the rotation of the ball screw shaft 8, the ball nut 5a receives a torque corresponding to the screw-engagement angle between the ball screw shaft 8 and the ball nut 5a. Therefore, accuracy in detection of the injection force by the load cell 5b is lowered.
An object of the present invention is to solve the above-mentioned problems in the conventional injection apparatus, and to provide an injection apparatus which can detect injection force with improved accuracy.
To achieve the above object, an injection apparatus according to the present invention comprises a cylinder member, an injection member, a first support member, drive means, a transmission shaft, a second support member, and load detection means. The injection member is disposed within the cylinder member such that the injection member can be advanced and retracted. The first support member supports the injection member such that the injection member can rotate. The transmission shaft is connected to the injection member such that the transmission shaft can rotate relative to the injection member and has a rotation transmission portion, to which rotation of the drive means is transmitted, as well as a motion conversion portion for converting rotational motion to linear motion. The second support member is adapted to allow relative rotation between the injection member and the transmission shaft. The load detection means is disposed between the first support member and the second support member.
In this injection apparatus, when the rotation of the drive means is transmitted to the transmission shaft via the rotation transmission portion, the rotational motion is converted to linear motion by the motion conversion portion, so that the injection member is advanced so as to perform injection. At this moment, the load detection means detects the injection force.
Since the load detection means is disposed between the first support member and the second support member, rotation of the injection member imparts no torque to the load detection means. Also, since the load detection means is connected to the transmission shaft via the second support member, rotation of the transmission shaft imparts no torque to the load detection means.
Therefore, accuracy in detection of injection force by the load detection means can be improved.
Another injection apparatus according to the present invention further includes a metering motor, and transmission means for transmitting rotation of the metering motor to the injection member.
Still another injection apparatus according to the present invention includes a heating cylinder, a screw, a support plate, an injection motor, a transmission shaft, a bearing box, and load detection means. The screw is disposed within the heating cylinder such that the screw can be advanced and retracted. The support plate supports the screw such that the screw can rotate. The transmission shaft is connected to the screw such that the transmission shaft can rotate relative to the screw and has a rotation transmission portion, to which rotation of the injection motor is transmitted, as well as a motion conversion portion for converting rotational motion to linear motion. The bearing box is adapted to allow relative rotation between the screw and the transmission shaft. The load detection means is disposed between the support plate and the bearing box.
In yet another injection apparatus according to the present invention, the rotation transmission portion is a spline shaft portion formed on the transmission shaft.
In yet another injection apparatus according to the present invention, the motion conversion portion is a ball screw shaft portion formed on the transmission shaft.